The polymorphonuclear neutrophil plays a prominent role in host resistance to foreign bacteria, including organisms involved in the development of periodontal disease. This is evidenced by the fact that patients with a number of different intrinsic neutrophil defects often present with particularly severe forms of periodontitis. In addition, pathogenic bacteria, including those from the oral cavity, can produce products which may either enhance or depress host immune responses. One such example of the latter case is the recently described low molecular weight substance present in Capnocytophaga culture supernatants which inhibits neutrophil chemotaxis. An important aspect of the proposed study will be to isolate this chemotaxis inhibitor and to characterize its chemical properties. We have also proposed studies to examine whether this substance, or other substances present in Capnocytophaga culture supernatants, influences other aspects of neutrophil function. Finally, we will characterize the interaction between selected Capnocytophaga strains and host mediation (antibody and/or complement) systems which facilitate clearance of these bacteria, either directly or cooperatively with neutrophils. These studies will provide fundamental information concerning a) mechanisms whereby oral bacteria may be effectively neutralized by host mediation systems and/or phagocytic cells and b) modulation of host responses by bacterial products which may contribute to the persistence of oral pathogens.